1. Field of the Invention
This invention relates generally to a binary weighted method for center pulse width modulation of signals for energizing electronic printer elements, and more particularly, to a simplified method and apparatus for centering the energization pulse for each electronic printer element on the most significant bit and locating half of each less significant bit relative to the centered most significant bit so as to form a mirror image on each side thereof.
2. Description of the Prior Art
Electronic devices for printing or recording an image on various photosensitive media are known in the art. Typically, such devices employ a linear array of light emitting diodes (LEDs). Relative movement between the array and the medium is established for effecting scanning of the array over the medium. Each LED may be selectively energized so that it produces a light pulse effective to expose corresponding pixels in the medium as it is advanced. Exposure occurs on a line by line basis in accordance with a variety of known control schemes.
Variations in the energization of the LEDs produce corresponding line by line variations in the exposure of the medium as it is scanned. Such variations may produce undesirable artifacts in the resulting image. Image resolution may be improved by decreasing such variations. Techniques designed to center the exposure within the pixels have been found to be effective.
An analog technique described in Reinten U.S. Pat. No. 4,712,116 employs analog comparator circuits connected to a signal generator to produce a uniformly decreasing and increasing signal and to buffers for storing a corrected image signal. The LEDs are energized with respect to the center of a time interval which corresponds to an image line parallel to the array of LEDs. Ayers et al. U.S. Pat. No. 4,750,010 attempts to digitally generate a set of center pulse width modulated wave forms employing a comparator which compares various preset counts with a variable count in order to vary the light output of the LEDs. Each system requires a complex and expensive array of comparators to achieve the desired result.
It is therefore an object of the present invention to provide a center pulse width modulated wave form employing a simple digital circuit.
It is another object of the present invention to provide a simplified method for effecting center pulse width modulation of printer elements.
It is another object of the present invention to substantially reduce or eliminate line to line artifacts associated with prior arrangements.